1. Field of the Invention
The present invention relates generally to a signaling method between peer-to-peer MAC-hs layers for HSDPA (High Speed Downlink Packet Access) in a CDMA (Code Division Multiple Access) communication system, and in particular, to a method for intermittently exchanging control information between MAC-hs entities on a Node B and a UE (User Equipment).
2. Description of the Related Art
In general, HSDPA (High Speed Downlink Packet Access) refers to HS-DSCH (High Speed-Downlink Shared Channel) for supporting high-speed downlink packet transmission and control channels related thereto in a CDMA communication system, and an apparatus, method and system therefor. In a CDMA communication system employing the HSDPA, the following three new techniques have been introduced in order to support the high-speed packet transmission.
First, AMCS (Adaptive Modulation and Coding Scheme) will be described. The AMCS adaptively determines a modulation technique and a coding technique of a data channel according to a channel condition between a cell and a user, thus increasing the overall utilization efficiency of the cell. A combination of the modulation technique and the coding technique is called “MCS (Modulation Coding Scheme),” and the MCS has a level of 1 to n. The AMCS adaptively determines a level of the MCS according to a channel condition of a user and a cell, thereby increasing the entire utilization efficiency.
Next, a description will be made of HARQ (Hybrid Automatic Retransmission Request), especially N-channel SAW HARQ (Stop and Wait Hybrid Automatic Retransmission Request). In the conventional ARQ, an ACK (acknowledgment) signal and a retransmitted packet are exchanged between a UE and a RNC (Radio Network Controller). However, in the HSDPA, an ACK and a retransmitted packet are exchanged between MAC (Medium Access Control) layers of a UE and a Node B. In addition, N logical channels are constructed to transmit a plurality of packets even in a state where ACK is not received. More specifically, in the existing SAW ARQ, a next packet cannot be transmitted before ACK for a previous packet is received. Therefore, it is necessary to await ACK, although it is possible to transmit a packet. However, in the N-channel SAW HARQ, a plurality of packets can be continuously transmitted on N number of channel even before ACK is received on a channel, thus increasing channel utilization efficiency. That is, if N logical channels are established between a UE and a Node B, and those logical channels can be identified by their channel numbers or their transmission time, the UE can determine a channel to which a packet received at a certain point belongs, and rearrange received packets in the right reception order.
Finally, FCS (Fast Cell Selection) will be described. The FCS allows an HSDPA UE (a UE employing the HSDPA) in a soft handover region to receive packets from only a cell in the best channel condition, thus reducing the overall interference. If another cell exhibits the best channel condition, the UE receives packets from the cell over an HS-DSCH, thus to minimize a transmission interruption time.
The HARQ technique newly proposed for the HSDPA service will be described in detail herein below.
A plurality of N-channel SAW HARQ protocol techniques have been proposed for the HSDPA, and those techniques can be classified into the following three techniques according to control information and their data transmission techniques in uplink/downlink. A first technique is a synchronous/synchronous transmission technique in which data retransmission over a downlink is synchronized to a channel over which original data was transmitted, and ACK/NACK transmission over an uplink is also synchronized with an HARQ channel. A second technique is an asynchronous/synchronous transmission technique, in which retransmission over a downlink is not restricted to a channel over which original data was transmitted, but is performed alternately asynchronously on different channels. A third technique is an asynchronous/asynchronous transmission technique, in which even ACK/NACK transmission over a downlink is not synchronized to a channel over which original data was transmitted.
FIG. 1 illustrates synchronous transmission by a Node B and synchronous/synchronous transmission by a UE for an HSDPA service. It is assumed in FIG. 1 that four (N) channels are used for transmission.
Referring to FIG. 1, a data block 101 received from an upper layer of a network (or a Node B, herein the terms “network” and “Node B” are used in the same meaning) is stored in a queue 102. The data block 101 stored in the queue 102 is provided to a channel sequencer (or distributor) 103, where the provided data block is distributed to transmitters 104, 105, 106 and 107 associated with the respective channels. The transmitters 104, 105, 106 and 107 sequentially transmit data blocks distributed by the channel distributor 103, and the transmitted data blocks are received at corresponding receivers 111, 113, 115 and 117 through a data channel 108. The data blocks received at the receivers 111, 113, 115 and 117 are provided to first to fourth retransmission decoders (or HARQ decoders) 112, 114, 116 and 118, respectively. The data blocks are analyzed by the corresponding HARQ decoders 112, 114, 116 and 118, and then transmitted to an upper layer of a UE.
While the data blocks are transmitted, corresponding signaling information is transmitted over a control channel. ACK/NACK information for the transmitted data blocks is transmitted from a UE to a network over a feedback channel. FIG. 1 is a diagram for explaining this concept, but an actual system may have a different structure. For example, though a plurality of the transmitters 104 to 107 and the receivers 111 to 117 are used in FIG. 1, one transmitter and one receiver can be used to transmit and receive a plurality of data blocks on a time division basis. In addition, although the data channel 108 is provided between the transmission side and the reception side, the transmission side has a memory buffer for the N HARQ channels. The reception side also has a combining memory for the N HARQ channels, and a buffer for gathering restored message sequences by a specified number and transmitting it to an upper layer.
The synchronous/synchronous transmission technique, a retransmission technique depending on a time relationship between data transmission over a downlink and ACK/NACK reception for the transmitted data, does not require sequence numbers. Therefore, in the downlink, a New/Continue (N/C) flag with a minimum of 1 bit transmitted over a control channel is needed to distinguish whether a transmitted data block is a new transmitted block or a retransmitted block, and ACK/NACK information on a feedback channel can also be transmitted with a minimum of 1 bit. This is because it is possible to distinguish data and ACK/NACK of each channel by time through synchronous transmission.
The asynchronous/synchronous transmission technique is similar in operation to the synchronous/synchronous transmission technique. However, since retransmission of a data block is allowed even for channels other than the channel over which the original data was transmitted, a downlink control channel further needs a channel processor number in addition to the 1-bit N/C flag. In the asynchronous/synchronous transmission technique, ACK/NACK information on a feedback channel is transmitted with a minimum of 1 bit, like in the synchronous/synchronous transmission technique.
The asynchronous/asynchronous transmission technique a channel processor number is needed in addition to the 1-bit N/C flag during transmission, and should transmit ACK/NACK information on a feedback channel with a sequence number for a downlink data block. This technique increases a signaling load, but has a relaxed restriction on transmission timing and a strong resistance to a possible error.
The above-described operation of the MAC layer for HSDPA employing the HARQ is a concept that has not been introduced in the existing mobile communication system, and the retransmission-related operation is performed in an RLC (Radio Link Control) layer.
FIG. 2 illustrates a multi-layered protocol structure in a W-CDMA (Wideband CDMA) communication system. In a mobile communication system, an RNC (Radio Network Controller) except a core network (or MSC (Mobile Switching Center)) is comprised of an RRC (Radio Resource Control) layer for controlling each element of a radio access network, an RLC (Radio Link Control) layer for managing a data packet received from an upper layer in a proper size, an MAC (Medium Access Control) layer for distributing/combining unit data blocks with a specified size into transport channels, and a physical layer (or Layer 1 (L1)) 230 for transmitting actual data blocks over a radio channel. The RRC layer belongs to Layer 3 (L3), and the RLC layer 210 belongs to Layer 2 (L2).
Signaling between a network and a UE is chiefly performed in the RRC and RLC entities. The RRC is designed to transmit a message procedure and control information for system information, RRC connection, and radio channel setup and reconfiguration. The RLC entity is designed to transmit a size of a window and ACK signaling of received data to control transmission and retransmission of data. However, the MAC entity has information for identifying a UE Id (Identification) and an upper layer logical channel in a header, but does not have a signaling message procedure between the network and the UE.
Since the W-CDMA communication system employing the HSDPA needs an HARQ function for the MAC layer in addition to an HARQ function for the RLC layer, its protocol structure should be modified correspondingly. Conventionally, the MAC entity is included in the RNC, so that the RLC and RRC entities are both installed in the RNC. However, in the HSDPA, a MAC-hs (MAC-high speed) entity is installed in a Node B transmission apparatus. The structural modification and the MAC entities will be separately described for a UE and a Node B (or network).
FIG. 3 illustrates a MAC structure of a UE. Referring to FIG. 3, MAC-d 330, a MAC entity for dedicated channels, performs a MAC function on dedicated logical channels such as a dedicated control channel (DCCH) and a dedicated traffic channel (DTCH). The dedicated logical channels, when they are mapped to a dedicated transport channel, are connected to a dedicated channel (DCH). When the dedicated logical channels are mapped to a common channel, data is transmitted to or received from MAC-c/sh 320 through a connection line to the MAC-d 330 and the MAC-c/sh 320. The MAC-c/sh 320, a MAC entity for common channels, exchanges data on common logical channels such as PCCH (Paging Control Channel), BCCH (Broadcast Control Channel), CCCH (Common Control Channel), CTCH (Common Traffic Channel) and SHCCH (Shared Control Channel) and exchange data with the MAC-d 330, with common transport channels such as PCH (Paging Channel), FACH (Forward Access Channel), RACH (Random Access Channel), CPCH (Common Packet Channel), USCH (Uplink Shared Channel) and DSCH (Downlink Shared Channel). Those entities receive a control command from the RRC entity through a control line shown in FIG. 2, and transmit a state report to the RRC. Such control information is achieved through MAC control.
The existing structure is comprised of only the MAC-d (MAC-dedicated) entity 330 for dedicated channels and the MAC-c/sh (MAC-common/shared) entity 320 for common (or shared) channels. However, as the existing structure adopts the HSDPA technique, it additionally introduces a MAC-hs (MAC-high speed) entity 310, thus providing a MAC function supporting HS-DSCH (High Speed-Downlink Shared Channel). The MAC-hs 310 is designed to be controlled by the RRC through MAC control. A message received from a Node B is restored into data through signal processing in a physical layer, and received at the MAC-hs entity 310 through an HS-DSCH transmission channel.
FIG. 4 illustrates a detailed structure of the MAC-c/sh. The MAC-c/sh will be described in more detail with reference to FIG. 4. The MAC-c/sh includes an ‘add/read UE Id’ part for adding/reading UE Id (Identification) to/from data exchanged with the MAC-d, a ‘Scheduling/Priority Handing’ part for transmission of transport channels such as RACH and CPCH, a ‘TF selection’ part for selecting the type of a Transport Format (TF), and an ‘ACS (Access Service Class) selection’ part. In addition, the MAC-c/sh includes a ‘TCTF MUX (Target Channel Type Field Multiplexing)’ part for attaching a header field for identifying common logical channels to data and multiplexing the header-attached data to respective transport channels, and a ‘TFC selection’ part for selecting TFC (Transport Format Combination) during the transmission of a transport channel USCH. As the HSDPA technique is introduced, the existing structure has a new connection to MAC-hs, while maintaining a function of the existing MAC-c/sh.
FIG. 5 illustrates a detailed structure of a MAC-hs layer newly defined as the HSDPA technique is introduced. The MAC-hs will be described in more detail with reference to FIG. 5. The MAC-hs performs an HARQ protocol function as a major HARQ function on an HS-DSCH channel. That is, the MAC-hs checks an error of a data block received from a radio channel, and performs generation and transmission of an ACK/NACK message to the MAC-c/sh. This entity has ‘Associated Uplink/Downlink Signaling’ radio control channels in order to frequently exchange HSDPA control information with UTRAN (UMTS (Universal Mobile Telecommunications System) Terrestrial Radio Access Network). This entity is controlled by the RRC.
FIG. 6 illustrates a MAC structure of a network. Referring to FIG. 6, MAC-d is designed to exchange data on dedicated logical channels DTCH and DCCH with a dedicated channel DCH and MAC-c/sh, like the MAC-d of the UE. However, the UTRAN includes a plurality of MAC-d's uniquely associated with the UEs, and the MAC-d's are connected to MAC-c/sh. The MAC-c/sh is also similar to that of the UE. These entities are all controlled by the RRC through MAC control.
As the HSDPA technique is introduced, the existing MAC structure includes a MAC-hs entity. The MAC-hs is designed to be arranged not in a radio network controller (RNC) but in a Node B. Therefore, data from an upper layer is transmitted through an interface lub between an RNC and a Node B, and a control message for the MAC-hs is also transmitted through the interface lub. The MAC-hs entity schedules transmission data, and is connected to a transmission channel HS-DSCH.
FIG. 7 illustrates a function of the existing MAC-c/sh. Referring to FIG. 7, the MAC-c/sh includes a ‘Flow Control MAC-c/sh/MAC-d’ function block for data exchange with the MAC-d, and a ‘TCTF MUX/UE Id MUX’ function block for identification between common logical channels PCCH, BCCH, SHCCH, CCCH, CTCH and dedicated logical channels from the MAC-d, and for UE identification. Further, the MAC-c/sh includes a ‘Scheduling/Priority Handling/Demux’ function block for common transport channels, and a ‘TFC selection’ function block for selecting TFC (Transport Format Combination) during data transmission over the common transport channels. When transmitting data over a transmission channel DSCH, the MAC-c/sh additionally includes a ‘DL: code allocation’ function block that allocates a code used for a downlink DSCH. As the HSDPA function is additionally introduced, the Flow Control function block is added to a route for transmitting data blocks to the MAC-hs.
FIG. 8 illustrates a function of the MAC-hs entity in more detail. Referring to FIG. 8, the MAC-hs entity has a function of processing data blocks on an HS-DSCH channel, and management on physical channel resources for HSDPA data is also processed by this entity. Data received at the MAC-hs from the MAC-c/sh of FIG. 7 is transmitted to a transmission channel HS-DSCH through a Flow Control function block for controlling a flow of the received data, an HARQ protocol function block for processing an HARQ-related protocol, a Scheduling/Priority Handling function block for determining a transmission point of data obtained by processing the received data according to the HARQ protocol, and a TFC selection function block. Unlike the MAC-d and the MAC-c/sh, the MAC-hs entity is arranged in a Node B, and directly connected to a physical layer. Therefore, the MAC-hs has ‘Associated Uplink/Downlink Signaling’ radio control channels in order to frequently exchange HSDPA-related control information with a UE through the physical layer.
Using the above-described entities, a control message needed to service high-speed packet data is generated and transmitted by RLC arranged in the Node B or the UE. Then, RLC of a reception side analyzes the control message and performs necessary operations according to the result of the analysis. A high-speed packet data service requires a short transmission unit and a rapid response. However, communication between RLC arranged in the RNC and RLC arranged in the UE has a long time delay, because the communication is performed through the RNC and the Node B. In addition, the HARQ technique is used for the high-speed packet data service. In this case, if it is necessary to reset a buffer memory for the HARQ, communication between MAC-hs of a transmission side and MAC-hs of a reception side must be performed. Therefore, the present invention provides a technique for enabling a message exchange between MAC-hs layers of a Node B and a UE.